Some Dinosaurs Didn’t Roar — They Cooed

July 19, 2016 | Erica Tennenhouse

Tyrannosaurus Rex
Photo credit: ScottRobertAnselmo/Wikipedia (C BY-SA 3.0)

Some dinosaurs cooed rather than roared.

Fossils can give us detailed insights into what extinct dinosaurs were like, but some things — sounds, for instance — just don’t fossilize.

Writing in the journal Evolution, a group of researchers has turned to living dinosaurs, i.e. birds, to gage how dinosaurs of the past might have vocalized.

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Most birds make noise with an open beak, but some can produce sounds with closed mouths by pushing air into a specialized vocal organ in their neck. These closed-mouth vocalizations are quiet, low-pitched, and often used to attract mates or defend territories. Dove cooing and the mating calls of ostriches are prime examples.

Closed-mouth ostrich mating call.

The researchers examined how closed-mouth vocal behavior is distributed across modern birds and closely related reptiles, and then used a statistical approach to reconstruct where this behavior first emerged in ancestral species.

"Our results show that closed-mouth vocalization has evolved at least 16 times in archosaurs, a group that includes birds, dinosaurs and crocodiles,” said study co-author Chad Eliason, from The University of Texas Jackson School of Geosciences, in a press release.

It is predominantly large-bodied species (the size of a dove or larger) that make sounds this way, likely because small species have a limited capacity to inflate their lungs.

Given that extinct dinosaurs were members of the archosaur group, and many had massive body size, the researchers believe “that the capacity for closed-mouth vocalization was present in at least some extinct nonavian dinosaurs.”

Closed-mouthed noises are a far cry from the resounding roars that one might expect from a large dinosaur.

"This makes for a very different Jurassic world,” commented study co-author Julia Clarke. “Not only were dinosaurs feathered, but they may have had bulging necks and made booming, closed-mouth sounds."

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